Relationship of the Hormone-Sensitive Lipase-Mediated Modulation of Cholesterol Metabolism in Individual Compartments of the Testis to Serum Pituitary Hormone and Testosterone Concentrations in a Seasonal Breeder, the Mink (Mustela vison)1

Abstract

The role of cholesterol differs in the two compartments of the testis. In the interstitial tissue, cholesterol is necessary for the synthesis of testosterone, whereas in the seminiferous tubules, membrane cholesterol content in developing germ cells will influence the gametes' fertility. Here we evaluate the hormone-sensitive lipase (HSL) modulation of the cholesterol metabolism in each compartment of the testis. Two HSL immunoreactive bands of 104- and 108-kDa were detected in Western blots performed with polyclonal anti-human HSL antibodies in the interstitial tissue (ITf)- and seminiferous tubule (STf)-enriched fractions generated from testes harvested at 30-day intervals during puberty and, in the adult mink, during the annual seasonal reproductive cycle. Epididymal spermatozoa expressed a 104-kDa HSL isoform, and HSL was active in these cells. Immunolabeling localized HSL to interstitial macrophages; Sertoli cells, where its distribution was stage specific; spermatids; and the equatorial segment of spermatozoa. Total HSL protein levels, specific enzymatic activity, and free cholesterol (FC):esterified cholesterol (EC) ratios varied concomitantly in STf and ITf and reached maximal values in the adult during the period of maximal spermatogenic activity. In STf, HSL-specific activity correlated with FC:EC ratios but not with triglyceride levels. In STf, high HSL-specific activity occurred concomitantly with high FSH serum levels. In ITf, HSL-specific activity was high during periods of low serum prolactin levels and high serum testosterone levels. The results suggest that 1) modulation of cholesterol metabolism in individual testicular compartments may be regulated by HSL isoforms expressed by distinct cells; 2) interstitial macrophages may be part of a system involved in the synthesis of steroid hormones and in the recycling of sterols in the interstitium, whereas in the tubules, recycling could be ensured by Sertoli cells; 3) there is distinctive substrate preference for testicular HSL; and 4) HSL may be the only cholesterol esterase in this location.

The predominance of one of the SR-BI isoforms is associated with increased esterified cholesterol levels not apoptosis in mink testis

“…Our results show that measurements generated with the N-EVAP Nitrogen Evaporator reflect real FC and EC levels and substantiate the data we had obtained previously by TLC (20).…”

“…The values are means 6 SEM from three independent experiments. with biotinylated anti-rabbit F(ab9) 2 (1:10,000 dilution) or antigoat IgG (1:2,000 dilution) and peroxidase-conjugated streptavidin (1:200 dilution) (20). Controls included either the first or the second antibody alone.…”

“…The lack of a C-terminal leucine amino acid decreased the surface expression of SR-BI in mouse hepatocytes, and the three C-terminal amino acids required for binding PDZK1 are lacking in SR-BII (76). Interestingly, hormone-sensitive lipase (20) and SR-BI expression are both upregulated in the tubules during stage X.…”

“…Besides the blood circulation, cholesterol within the tubules themselves originates from the phagocytosis of lipidcontaining residual bodies, lipid-rich cells, and apoptotic germ cells or their cell membrane remnants, which can represent up to 50% of cell loss in normal testis (17,18). The observation that free cholesterol (FC) concentration in the interstitial tissue equals that in tubules (19,20) entails factors regulating cholesterol influx and efflux to maintain equilibrium.…”

HSL-knockout mouse testis exhibits class B scavenger receptor upregulation and disrupted lipid raft microdomains

“…HSL is localized to elongated spermatids and Sertoli cells guinea pig and mink testis ( 8,33 ). In the rat, HSL is only located in the seminiferous tubules (Sertoli and spermatogenic cells) ( 34 ), whereas in the normal human testis, HSL is detected in seminiferous tubules and Leydig cells ( 35 ).…”